The transmission having the main section and the auxiliary section is widely used in heavy-duty vehicles. A synchronizer is provided in the auxiliary section, and mostly adopts a lock pin-type synchronizer including a higher gear conical ring and a lower gear conical ring which are arranged at both sides of a sliding gear sleeve. A higher gear lock pin is fixed to one side of the higher gear conical ring. A lower gear lock pin is fixed to one side of the lower gear conical ring. Pin holes corresponding to the higher gear lock pin and the lower gear lock pin are arranged on the sliding gear sleeve. At present, in the conventional lock pin-type automobile synchronizer, the higher gear side components are configured to substantially have the same strength as the lower gear side components, that is, the higher gear lock pin has the same number and the completely or approximately same diameter as the lower gear lock pin. However, for the synchronizer in the auxiliary section, it will take a relatively long synchronizing time to engage the lower gear, that is, the synchronizer will be loaded for a long time when engaging the lower gear. Thus, compared with the higher gear side components, the associated lower gear side components have a shorter fatigue life, such that the lower gear lock pin tends to be ruptured or loosed untimely and thus the whole synchronizer becomes failure untimely.